As to a rotor core formed by a plurality of circumferentially divided rotor core materials, technology as mentioned in Patent document 1 is commonly known. The technology mentioned in Patent document 1 is such that these rotor core materials are connected to each other with some play provided via junctions in such manner as to be positioned in an annular fashion. And, in this condition, they are set in a mold and integrated into one piece by a steel frame and resin in the mold.
Due to the technology mentioned in Patent document 1, when rotor core materials are set in a mold, rotor core materials are connected to each other with some play provided via junctions, and therefore, the rotor core materials can be set in the mold while providing clearance between the mold and the rotor core. In this way, it is possible to improve the workability. Also, when resin is used for the purpose of molding, the rotor core is pressed in the direction of inner diameter due to the resin molding pressure, causing the play between rotor core materials to be removed, and it is possible to secure the dimensional accuracy.
However, when a rotor core formed by rotor core materials as mentioned in Patent document 1 is used, gaps are generated between rotor core materials. As a result, abrupt change of the magnetic flux is generated between the rotor core material and the gap. This gives rise to the problem of increase of cogging torque and torque ripple.
Patent document 1 Unexamined Japanese Patent Publication 2006-187176